Position sensors in the form of angle encoders of the type having a magnetic graduation with a code structure have been known in the prior art. Applicant's German Patent Publication No. DE 44 42 371 A1 discloses distinguishing such graduations by a multi-track alternating magnetization of a dynamically balanced body which rotates proportionally in relation to the rotary movement supplied to the angle encoder. During rotation, this alternating magnetization is detected by static Hall elements which scan every track of the graduation and output an absolute position signal.
European Patent Publication No. EP 0 331 828 A1 discloses a multi-turn sensor which is basically composed of two measuring systems, an incremental optical measuring system and a magnetic detector. The incremental optical measuring system determines the exact position of an optical graduation during one revolution of the graduation and the magnetic detector determines the number of revolutions of the optical graduation. By using such a multi-turn sensor it is possible for a control unit to determine the absolute position of the optical graduation even after several revolutions of the optical graduation. When the multi-turn sensor is connected to a supply voltage, the stored number of revolutions and the stored incremental value are output so the absolute position is output immediately after power is supplied. To reduce the amount of electricity used by the multi-turn sensor, magneto-resistive elements having several hundred K.OMEGA. of internal resistance are used and additional resistors are connected in series. In addition, digital component groups produced by CMOS technology are used.
A disadvantage of such a system is that the electrical power requirements of CMOS components increase with frequency so that at high processing speeds the requirement for electrical power is large. In addition, special magneto-resistive elements having a high internal resistance are required which makes further elaborate processing of their output signals necessary which introduces an increased sensitivity to noise in the system.
U.S. Pat. Nos. 4,780,703 and 4,796,005 disclose an incremental angle encoder where the position, or respectively the angle of rotation, is determined by an optical measuring system. The optical measuring system has a light source, a static graduation and a rotating graduation, as well as light-sensitive component groups with their associated electronic evaluation devices. To save energy, the light source and the electronic evaluation devices are connected with a supply voltage only long enough as is required to determine the position within the smallest graduation period. These component groups are otherwise disconnected from the energy supply.
A disadvantage with such a system is that because of the considerably higher current strengths required by the entire circuit arrangement while the light source and the electronic evaluation device are coupled to the supply voltage for only a short-time, interference often occurs.